Astronomer: Proponents of the hypothesis that life evolved extraterrestrially and drifted here in spores point out that, 3.8 billion years ago, Earth was bombarded by meteorites that would have destroyed any life already here. Yet 3.5 billion years ago, Earth had life forms complex enough to leave fossil remains. Such life could not have evolved here in the 0.3 billion years following the meteorite bombardments, they claim. There is good reason to regard their hypothesis as false, however, for they merely offer empirical arguments against the view that life evolved on Earth; neither they nor anyone else has provided positive support for the extraterrestrial-spore theory of the origin of terrestrial life.

The reasoning in the astronomer’s argument is flawed because the argument